Displacement control system for variable displacement type hydraulic pump

ABSTRACT

In a displacement control system for a variable displacement type hydraulic pump for supplying a discharge pressurized fluid of the variable displacement type hydraulic pump to an actuator via a direction control valve and then controlling a displacement of said variable displacement type hydraulic pump for maintaining a pressure difference between a discharge pressure of said variable displacement type hydraulic pump 1 and a load pressure at a portion between a direction control valve and an actuator, wherein an inlet side pressure of said direction control valve is detected as said discharge pressure.

FIELD OF THE INVENTION

The present invention relates to a displacement control system for avariable displacement type hydraulic pump.

BACKGROUND ART

As a displacement control system for a variable displacement typehydraulic pump, a system performing control with a pump dischargepressure and a load pressure, as shown in FIG. 1, for example, has beenknown.

Namely, a direction control valve 3 is provided in a discharge path 2 ofa variable displacement type hydraulic pump 1 (hereinafter referred toas variable hydraulic pump) and then a pressurized fluid is supplied toan actuator 4 via the direction control valve 3. A displacement controlcylinder 6 is provided for driving a displacement control member 5, suchas a swash plate and so forth of the variable hydraulic pump 1. Onechamber 6a of the displacement control cylinder 6 is connected to adischarge path 2 via a first circuit 7. The other chamber 6b isselectively connected to a second circuit 9 (connected to the dischargepath 2) via a pump port side of a displacement control valve 8 and to atank circuit 10 via a drain port side of the displacement control valve.A first pressure receiving portion 11 of the displacement control valve8 is connected to the second circuit 9, and the second pressurereceiving portion 12 is connected to a load pressure detecting circuit14 which is connected to the actuator 4. The displacement control valve8 is forced to a communicating position A by a pressurized fluid (pumpdischarge pressure P₁) acting on the first pressure receiving portion11, and to a drain position B by a pressurized fluid (load pressureP_(LS)) acting on the second pressure receiving portion 12 and a spring13. It should be noted that a circuit for returning the pressurizedfluid from the actuator 4 to a tank is neglected for simplification ofthe drawing.

With the displacement control system, the displacement control valve 8is placed at the communicating position A when a pressure differenceΔP_(LS) between the pump discharge pressure P₁ and the load pressureP_(LS) becomes higher to actuate the displacement control cylinder 6 inX direction to operate the displacement control member 5 in a directionfor smaller displacement, and is placed at the drain position B when apressure difference ΔP_(LS) between the pump discharge pressure P₁ andthe load pressure P_(LS) becomes lower to actuate the displacementcontrol cylinder 6 in Y direction to operate the displacement controlmember 5 in a direction for greater displacement. In practice, thedisplacement control member 5 is controlled for establishing equilibriumbetween the pressure difference ΔP_(LS) of the pump discharge pressureP₁ acting on the first pressure receiving portion and the load pressureP_(LS) acting on the second pressure receiving portion 12 and the loadof the spring 13. Namely, the displacement of the variable displacementpump 1 is controlled so that the pressure difference between the pumpdischarge pressure P₁ and the load pressure P_(LS) is maintainedconstant.

With such displacement control system, when the open area of thedirection control valve 3 is reduced while a constant flow rate ofpressurized fluid flows (at this time the pressure difference ΔP_(LS) ismaintained constant), the pressure difference ΔP_(LS) becomes greater.Therefore, the displacement control member 5 is actuated in thedirection for smaller displacement until the ΔP_(LS) returns to theinitial value. On the other hand, when the open area of the directioncontrol valve 3 is increased, the pressure difference ΔP_(LS) becomessmaller. Therefore, the displacement control member 5 is actuated in thedirection for greater displacement until the pressure difference ΔP_(LS)returns the initial value. Accordingly, the displacement of the variablehydraulic pump 1 becomes a value depending upon the open area of thedirection control valve. Namely, the displacement is controlled tomaintain a pressure loss (the pressure difference ΔP_(LS) between thepump discharge pressure and the load pressure) upon flowing of thepressurized fluid through the direction control valve 3 constant.

However, in the conventional control system as set forth above, thedisplacement control cylinder 6 and the displacement control valve 8 areprovided within a single pump body 15. In this connection, the first andsecond circuits 7 and 9 are also provided in the pump body 15. On thefirst pressure receiving portion 11 of the displacement control valve 8,the pressure of a pump discharge portion 16 acts as the pump dischargepressure P₁.

Therefore, the load pressure P_(LS) acting on the second pressurereceiving portion 12 of the displacement control valve 8 is lower thanthe pump discharge pressure P₁ acting on the first pressure receivingportion 11 in the extent of a sum of the pressure loss caused when thepressurized fluid flows through the direction control valve 3 and apressure loss caused when the pressurized fluid flows through thedischarge path 2 connecting the hydraulic pump 1 and the inlet of thedirection control valve 3. Namely, since the displacement control valve8 is affected by the pressure loss due to flow resistance in thedirection control valve 3 and the pressure loss due to path resistancein the discharge path 2, the displacement of the variable hydraulic pump1 cannot be controlled to maintain the pressure loss caused when thepressurized fluid flows through the direction control valve 3. Thus, itbecomes impossible to accurately supply the flow rate depending upon theopen area of the direction control valve 3 to the actuator 4.Particularly, when large flow rate of pressurized fluid is to be flown,the pressure loss in the discharge path of the pump is increased toreduce the supply flow rate to the actuator 4.

It is an object of the present invention to provide a displacementcontrol system for a variable displacement type hydraulic pump, whichcan control a displacement without being influenced by a pressure lossof a discharge path of the variable displacement type pump and namely,can control the displacement of the variable displacement type hydraulicpump so that the pressure loss at a direction control valve ismaintained constant.

DISCLOSURE OF THE INVENTION

In order to accomplish the above-mentioned object, in accordance withthe present invention, there is provided a displacement control systemfor a variable displacement type hydraulic pump for supplying adischarge pressurized fluid of the variable displacement type hydraulicpump to the actuator via the direction control valve and thencontrolling a displacement of the variable displacement type hydraulicpump for maintaining a pressure difference between a discharge pressureat a portion between the variable displacement type hydraulic pump 1 anda load pressure of a direction control valve and an actuator, wherein aninlet side pressure of the direction control valve is detected as thedischarge pressure.

With the construction set forth above, the pressure at the inlet side ofthe direction control valve is detected as the pump discharge pressureand the displacement of the variable displacement type hydraulic pump iscontrolled to maintain the pressure difference between the pumpdischarge pressure and the load pressure constant. Therefore, thedisplacement can be controlled without being affected by the pressureloss in the discharge path of the variable displacement type hydraulicpump. Namely, the displacement of the variable displacement type pumpcan be controlled so that the pressure loss in the direction controlvalve becomes constant.

On the other hand, in the construction set forth above, it is desirablethat the displacement control system comprises a displacement controlmember of the variable displacement type hydraulic pump, a displacementcontrolling cylinder actuating the displacement control member and adisplacement control valve supplying the pressurized fluid to thedisplacement control cylinder, wherein the displacement control valvebeing actuated in a direction for smaller displacement in response tothe pressure acting on the first pressure receiving portion and in adirection for greater displacement in response to the pressure acting onthe second pressure receiving portion, and

that a pump discharge pressure detecting circuit connected to the firstpressure receiving portion is connected to the inlet side of thedirection control valve and a load pressure detecting circuit connectedto the second pressure receiving portion is connected to the outlet sideof the direction control valve.

Also, an orifice may be provided in the pump discharge pressuredetecting circuit for preventing the pressure acting on the firstpressure receiving portion of the displacement control valve fromvarying abruptly to stabilize the displacement control valve.

Furthermore, in the construction set forth above,

the direction control valve may include a valve body, a spool boreformed in the valve body and having a pump port and an actuator port,and a spool disposed within the spool bore and establishing and blockingcommunication between the pump port and the actuator port,

valve bodies of a plurality of the direction control valves may becombined with mutually communicating respective pump ports, thedischarge path of the variable hydraulic pump may be connected to thepump port of one of the valve bodies of the plurality of directioncontrol valves, and the pump discharge pressure detecting circuit may beconnected to the pump port of another valve body of the plurality ofdirection control valves.

Also, a cover having a fluid conduit communicated with the pump port maybe coupled with the another valve body, and the pump discharge pressuredetecting circuit is connected to the fluid conduit. A maximum loadpressure detecting circuit may be provided in a circuit communicatingthe actuator port and the actuator for supplying the maximum loadpressure detected by the maximum load pressure detecting circuit to theload pressure detecting circuit. An orifice may be provided in the pumpdischarge pressure detecting circuit.

In the construction set forth above, it is possible that

the direction control valve may include a valve body, a spool boreformed in the valve body and having a pump port and an actuator port,and a spool disposed within the spool bore and establishing and blockingcommunication between the pump port and the actuator port,

valve bodies of a plurality of the direction control valves may becombined with mutually communicating respective pump ports to form ablock,

a confluence valve having a valve body and two input ports formed in thevalve body and communicated with each other is provided,

two blocks are connected at both sides of the valve body of theconfluence valve with communicating respective pump ports of the twoblocks and the two inlet ports,

thus the discharge paths of respective variable displacement typehydraulic pumps connected to respective of the two blocks are connectedto the two inlet ports respectively, and pump discharging pressuredetecting circuits of respective displacement control system connectedto respective of the two blocks are connected to the pump ports of thetwo blocks respectively.

With this construction,

the discharged pressurized fluid of two variable displacement typehydraulic pumps can be combined and supplied to one actuator.

Furthermore, a cover having the fluid conduits communicated with thepump ports may coupled with the valve body in each block, located at theopposite side of the confluence valve, and each of the pump dischargepressure detecting circuits may be connected to each fluid conduit.Also, the a maximum load pressure detecting circuit may be provided in acircuit communicating the actuator port and the actuator so as to supplythe maximum pressure detected by the maximum pressure detecting circuitto each of the load pressure detecting circuits.

In addition to the construction set forth above, it is desirable that aninlet pressure detecting port is formed in the valve body of thedirection control valve in one of the block, located remote from theconfluence valve, which inlet pressure detecting port communicates withthe pump port only when the pump port is communicated with the actuatorport, the inlet pressure detecting port is connected to the pumpdischarge pressure detecting circuit of the displacement control systemconnected to the other block, and an orifice is provided in the pumpdischarge pressure detecting circuit.

With the construction set forth above, it can avoid lowering of thedisplacement of the variable displacement type hydraulic pump due to thepressure loss by flowing the discharged pressurized fluid of thevariable displacement pump connected to one block through pump ports ofa plurality of direction control valves in the other block or throughthe communicating portion of the confluence valve. Therefore, thepressurized fluid corresponding to a controlling pressure difference canbe supplied to the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given herebelow and from the accompanying drawings of thepreferred embodiment of the invention, which, however, should not betaken to be limitative to the present invention, but are for explanationand understanding only.

In the drawings:

FIG. 1 is hydraulic circuit diagram of the conventional displacementcontrol system for a variable displacement type hydraulic pump;

FIG. 2 is a hydraulic circuit diagram showing the first embodiment of adisplacement control system for the variable displacement type hydraulicpump according to the present invention;

FIG. 3 is a hydraulic circuit diagram showing the second embodiment;

FIG. 4 is a hydraulic circuit diagram showing the third embodiment;

FIG. 5 is a hydraulic circuit diagram showing the fourth embodiment; and

FIG. 6 is a detailed sectional view of a direction control value havinginlet pressure detecting port, in the fourth embodiment.

BEST MODE FOR IMPLEMENTING INVENTION

The preferred embodiments of displacement control systems for variabledisplacement type hydraulic pump according to the present invention willbe discussed hereinafter with reference to the accompanying drawings.

The first embodiment of the present invention will be discussed withreference to FIG. 2. It should be noted that like components common tothe foregoing prior art will be represented by the like referencenumerals and the discussion therefor will be neglected. Also, forsimplification of the drawing, the circuit for returning the pressurizedfluid from the actuator 4 to the tank will be neglected.

In the shown embodiment, a pump discharge pressure detecting circuit 17is provided. One end of the circuit 17 is connected to the firstpressure receiving portion 11 of the displacement control valve 8 andthe other end thereof is connected to the inlet side of the directioncontrol valve 3 so that the pressure at the inlet side of the directioncontrol valve 3 acts on the first pressure receiving portion 11 of thedisplacement control valve 8 as the pump discharge pressure.

Since the shown embodiment is constructed as set forth above, the pumpdischarge pressure P₁ acting on the first pressure receiving portion 11of the displacement control valve 8 is not affected to the pressure lossof the pump discharge path of the hydraulic pump 1. Accordingly, thepressure difference ΔP_(LS) between the pump discharge pressure P₁acting on the first pressure receiving portion 11 of the displacementcontrol valve 8 and the load pressure P_(LS) acting on the secondpressure receiving portion 12, becomes substantially equal to thepressure loss in the direction control valve 3. As a result, thedisplacement of the variable hydraulic pump 1 can control so as tomaintain the pressure loss upon flowing through the direction controlvalve 3 constant.

It should be noted that a orifice 18 may be provided in the pumpdischarge pressure detecting circuit 17 for avoiding abrupt variation ofthe pressure acting on the first pressure receiving portion 11 of thedisplacement control valve 8 to stabilize the displacement control valve8.

FIG. 3 shows the second embodiment.

In the shown embodiment, the direction control valve 3 is constructed asfollows. First and second pump ports 21 and 22, first and secondactuator ports 23 and 24, and first and second tank ports (not shown)are formed in the valve body 20. Then, in a not shown spool bore of thevalve body 20, a not shown spool is inserted. Thus, the directioncontrol valve is constructed to shut off respective ports 21, 22, 23, 24and so forth at a neutral position of the spool, and to establishes acommunication between the first or second pump ports 22 and the first orsecond actuator ports 23, 24 and a communication between the second orfirst actuator port 24, 23 and second or first tank port at a first orsecond position of the spool.

Then, valve bodies 20 of a plurality of direction control valves 3 arecombined in parallel so that respective first pump ports 21 and secondpump ports 22 are communicated, and the discharge path 2 of the variablehydraulic pump 1 is connected with first and second pump ports 21 and 22of one of the direction control valves 3. A cover 25 is connected withthe valve body 20 of the other direction control valve 3. The cover 25is formed with fluid conduits 26 communicating with the first and secondpump ports 21 and 22. The pump discharge pressure detecting circuit 17is connected to the fluid conduits 26.

Furthermore, in a circuit communicating the first and second actuatorports 23 and 24 of respective direction control valves 3 and respectiveactuators 4, a maximum load pressure detecting circuit 27 is provided.The maximum load pressure detecting circuit 27 is adapted to compareload pressures of respective actuators 4 by a plurality of shuttlevalves and whereby detect the highest load pressure. The detectedhighest load pressure is supplied to the load pressure detecting circuit14.

FIG. 4 shows the third embodiment.

In the shown embodiment, the discharge paths 2 of two variable hydraulicpumps 1 and 1 are connected to first and second inlet ports 32 and 33 ofa valve body 31 of a confluence valve 30 having a confluence passage 34.At the left side of the confluence valve 30, a block which is formed bycombining valve bodies 20 of first, second and third direction controlvalves 3₁, 3₂ and 3₃, is coupled. On the other hand, at the right sideof the confluence valve, a block which is formed by combining valvebodies 20 of the fourth to tenth direction control valves 3₄ to 3₁₀ iscoupled. Also, to the fluid conduit 26 of the cover 25 coupled with thevalve body 20 of the first direction control valve 3₁, the pumpdischarge pressure detecting circuit 17 of one of the hydraulic pumps 1is connected. To the fluid conduit 26 of the cover 25 coupled with thevalve body 20 of the tenth direction control valve 3₁₀, the pumpdischarge pressure detecting circuit 17 of the other hydraulic pump 1 isconnected.

Since the shown embodiment is constructed as set forth above, in acircuit communicating the first and second actuator ports 23 and 24 ofrespective direction control valves 3 and respective actuators 4,maximum load pressure detecting circuit 27 is provided. The loadpressure detecting circuit 14 is connected with the maximum loadpressure detecting circuit 27 so that the maximum load pressure of thefirst to tenth direction control valves 3₁ to 3₁₀ is supplied to theload pressure detecting circuit 14.

Since the shown embodiment is constructed as set forth above, thedischarged pressurized fluid of one variable hydraulic pump 1 and thedischarged pressurized fluid of the other variable hydraulic pump 1 arecombined in the confluence valve 30 and supplied to respective actuators4 from respective direction control valves 3.

It should be noted that, in FIG. 4, the first direction control valve 3₁is a turning valve supplying the pressurized fluid of the turninghydraulic motor of a power shovel, similarly, the second directioncontrol valve 3₂ is a left traveling valve supplying the pressurizedfluid to a left side traveling hydraulic motor, the third directioncontrol valve 3₃ is an arm valve supplying the pressurized fluid to anarm cylinder, the fourth, fifth and sixth direction control valves 3₄,3₅ and 3₆ are boom valve, right traveling valve and bucket valvesupplying pressurized fluid to a boom cylinder, a right side travelinghydraulic motor and a bucket cylinder, respectively, the seventhdirection control valve 3₇ is an auxiliary boom and arm valve assistingsupply of the pressurized fluid to the boom cylinder and the armcylinder, the eighth, ninth and tenth direction control valves 3₈, 3₉and 3₁₀ are service valves for supplying the pressurized fluid toactuators to be added to normal power shovel of a crusher as attachment,for example, double holding boom cylinder, rotary arm and so forth.Respective actuators supplied the pressurized fluid by respectiveservice valves are not required fine operation but requires large flowrate.

On the other hand, in FIG. 4, when the pressurized fluid is suppliedfrom the left and right variable hydraulic pumps 1, 1 to the actuators 4with the service valve constituted of the tenth direction control valve3₁₀ which is most distant from the confluence valve 30, a pressure losscorresponding to flow resistances of the pressurized fluid flowingthrough first or second pump paths 21, 22 of the fourth to ninthdirection control valves 3a from the confluence valve 30, in terms ofthe inlet pressure of the third direction control valve 3₁₀. Also, inFIG. 4, concerning the pressurized fluid supplied from the left sidevariable hydraulic pump 1, there is the pressure loss due to flowresistance when the pressurized fluid flows through the communicationpath 34 of the confluence valve 30.

At this time, the pressure of the pump discharge pressure detectingportion A controlling the displacement of the right side variablehydraulic pump 1 is substantially equal to the inlet pressure of thetenth direction control valve 3₁₀ and thus is not affected by the flowresistance of the path. However, the pressure of the pump dischargepressure detecting portion B controlling displacement of the left sidevariable hydraulic pump 1 becomes higher than the inlet pressure of thetenth direction control valve 3₁₀ in the extent of a sum of the pressureloss through the fourth to ninth direction control valves 10₄ to 10₉ andthe pressure loss of the communication path 34 of the confluence valve30. It should be appreciated that since the pressurized fluid does notflow through the first and second pump ports 21 and 22 of the first tothird direction control valves 3₁ to 3₃, the pressure at the pumpdischarge pressure detecting portion B is equal to the pressure at thesecond inlet port 33. Accordingly, the pressure difference ΔP_(LS)between the first and second pressure receiving portions 11 and 12 ofthe displacement control valve 8 controlling displacement of the leftside variable hydraulic pump becomes greater in the extent correspondingto the pressure loss set forth above, and the displacement of the leftside variable hydraulic pump 1 is decreased in the corresponding amount.Therefore, it is possible that the flow rate of the pressurized fluidsupplied to the actuator 4 from the service valve constituted of thetenth direction control valve 3₁₀ is decreased and thus the demand ofthe service valve cannot be satisfied.

FIG. 5 shows the fourth embodiment solving the drawback in the thirdembodiment.

In the shown embodiment, an inlet pressure detecting port 28 is formedin the valve body 20 of the tenth direction control valve 3₁₀. Only whenthe first pump port 21 is communicated with the first actuator port 23or when the second pump port 22 is communicated with the second actuatorport 24 by shifting the not shown spool, the first pump port 21 iscommunicated with the inlet pressure detecting port 28. The inletpressure detecting port 28 is connected to the left side pump dischargepressure detecting circuit 17 through a circuit 29.

On the other hand, in the vicinity of the pump discharge pressuredetecting portion B of the left side pump discharge pressure detectingcircuit 17, the orifice 18 is provided so that the pressure of the fluidconduit 26 upon actuation of the tenth direction control valve 3₁₀ doesnot affect for the circuit 29 or the first pressure receiving portion 11of the displacement control valve 8.

Thus, the inlet pressure of the tenth direction control valve 3₁₀ actson the first pressure receiving portion 11 of the displacement controlvalve 8 of the left side variable hydraulic pressure pump 1 to preventthe displacement from being decreased. In conjunction therewith, itbecomes possible to avoid lack of displacement of the left side variablehydraulic pump 1 caused by the sum of the flow resistance (pressureloss) in flowing through the pump port of a plurality of directioncontrol valves and the flow resistance of the communication path of theconfluence valve. Thus, the demand of the service valve constituted ofthe tenth direction control valve 3₁₀ can be satisfied to permit supplyof necessary flow rate of the pressurized fluid to the actuator 4.Namely, it becomes possible to supply the pressurized fluid in the flowrate corresponding to a controlling pressure difference to the actuator4.

FIG. 6 is a detailed sectional view of the fourth embodiment of thedirection control valve 3 with the inlet pressure detecting port 28. Ina spool bore 40 of the valve body 20 of the direction control valve 3,the first and second pump port 21, 22, the first and second actuatorports 23, 24, first and second outlet ports 41, 42, first and secondtank ports 43, 44 and the inlet pressure detecting port 28 are formed.In a spool 45 disposed within the spool bore 40, first and second inletside small diameter portions 46, 47, first and second outlet side smalldiameter portions 48, 49 and an inlet pressure detecting small diameterportion 50 are formed. Thus, by shifting the spool 45 from the shownneutral position toward left to communicate the first pump port 21 withthe first outlet port 41 and communicate the second actuator port 24with the second tank port 44, the pressurized fluid in the first outletport 41 forces a check valve 51 to open to flow into the first actuatorport 23. At the same time, by communication of the first pump port 21with the inlet pressure detecting port 28 via the inlet pressuredetecting small diameter portion 50, the inlet pressure is detected.

Although the invention has been illustrated and described with respectto exemplary embodiment thereof, it should be understood by thoseskilled in the art that the foregoing and various other changes,omissions and additions may be made therein and thereto, withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention should not be understood as limited to thespecific embodiment set out above but to include all possibleembodiments which can be embodies within a scope encompassed andequivalents thereof with respect to the feature set out in the appendedclaims.

We claim:
 1. A displacement control system for a variable displacementtype hydraulic pump for supplying a discharge pressurized fluid of saidvariable displacement type hydraulic pump to an actuator via a directioncontrol valve and then controlling a displacement of said variabledisplacement type hydraulic pump for maintaining a pressure differencebetween a discharge pressure of said variable displacement typehydraulic pump and a load pressure at a portion between said directioncontrol valve and said actuator,said system comprising a displacementcontrol member of said variable displacement type hydraulic pump, adisplacement controlling cylinder actuating said displacement controlmember and a displacement control valve supplying the pressurized fluidto said displacement control cylinder, wherein an inlet side pressure ofsaid direction control valve is detected as said discharge pressure,said displacement control valve is actuated in a direction for smallerdisplacement in response to the pressure acting on a first pressurereceiving portion of said valve and in a direction for greaterdisplacement in response to pressure acting on a second pressurereceiving portion of said valve, a pump discharge pressure detectingcircuit connected to said first pressure receiving portion is connectedto the inlet side of said direction control valve and a load pressuredetecting circuit connected to said second pressure receiving portion isconnected to the outlet side of said direction control valve, and anorifice is provided in said pump discharge pressure detecting circuit.2. A displacement control system for a variable displacement typehydraulic pump for supplying a discharge pressurized fluid of saidvariable displacement type hydraulic pump to an actuator via a directioncontrol valve and then controlling a displacement of said variabledisplacement type hydraulic pump for, maintaining a pressure differencebetween a discharge pressure of said variable displacement typehydraulic pump and a load pressure at a portion between said directioncontrol valve and said actuator,said system comprising a displacementcontrol member of said variable displacement type hydraulic pump, adisplacement controlling cylinder actuating said displacement controlmember and a displacement control valve supplying the pressurized fluidto said displacement control cylinder, wherein an inlet side pressure ofsaid direction control valve is detected as said discharge pressure,said displacement control valve is actuated in a direction for smallerdisplacement in response to the pressure acting on a first pressurereceiving portion of said valve and in a direction for greaterdisplacement in response to pressure acting on a second pressurereceiving portion of said valve, a pump discharge pressure detectingcircuit connected to said first pressure receiving portion is connectedto the inlet side of said direction control valve and a load pressuredetecting circuit connected to said second pressure receiving portion isconnected to the outlet side of said direction control valve, and saiddirection control valve includes a valve body, a spool bore formed insaid valve body and having a pump port and an actuator port, and a spooldisposed within said spool bore and establishing and blockingcommunication between said pump port and said actuator port, valvebodies of a plurality of said direction control valves are combined withmutually communication respective pump pods, said discharge path of saidvariable hydraulic pump is connected to the pump port of some of thevalve bodies of said plurality of direction control valves, and saidpump discharge pressure detecting circuit is connected to the pump portof another valve body of said plurality of direction control valves. 3.A displacement control system for a variable displacement type hydraulicpump as set forth in claim 2, wherein a cover having a fluid conduitcommunicated with said pump port is coupled with said another valvebody, and said pump discharge pressure detecting circuit is connected tosaid fluid conduit.
 4. A displacement control system for a variabledisplacement type hydraulic pump as set forth in claim 2 or 3, wherein amaximum load pressure detecting circuit is provided in a circuitcommunicating said actuator port and said actuator for supplying themaximum load pressure detected by said maximum load pressure detectingcircuit to said load pressure detecting circuit.
 5. A displacementcontrol system for a variable displacement type hydraulic pump as setforth in any one of claims 2 or 3, wherein an orifice is provided insaid pump discharge pressure detecting circuit.
 6. A displacementcontrol system for a variable displacement type hydraulic pump as setforth in claim 2, which further includes a confluence valve having avalve body and two inlet ports formed in said valve body andcommunicated with each other, two blocks respectively formed bycombining the valve blocks of said plurality of direction control valvesare connected at both sides of said valve body of said confluence valvewith communicating respective pump ports of said two blocks and said twoinlet ports, discharge paths of respective variable displacement typehydraulic pumps connected to respective of said two blocks are connectedto said two inlet ports respectively, and pump discharging pressuredetecting circuits of respective displacement control system connectedto respective of said two blocks are connected to the pump ports of saidtwo blocks respectively.
 7. A displacement control system for a variabledisplacement type hydraulic pump as set forth in claim 6, wherein aninlet pressure detecting port is formed in the valve body of saiddirection control valve in one of said block, located remote from saidconfluence valve, which inlet pressure detecting port communicates withsaid pump port only when said pump port is communicated with saidactuator port, said inlet pressure detecting port is connected to saidpump discharge pressure detecting circuit of said displacement controlsystem connected to the other block, and an orifice is provided in saidpump discharge pressure detecting circuit.
 8. A displacement controlsystem for a variable displacement type hydraulic pump as set forth inclaim 6 or 7, a cover having the fluid conduits communicated with saidpump ports is coupled with the valve body in each block, located at theopposite side of said confluence valve, and each of said pump dischargepressure detecting circuits is connected to each fluid conduit.
 9. Adisplacement control system for a variable displacement type hydraulicpump as set forth in any one of claims 6 or 7, wherein a maximum loadpressure detecting circuit is provided in a circuit communicating saidactuator port and said actuator for supplying the maximum load pressuredetected by said maximum load pressure detecting circuit to said loadpressure detecting circuit.